A fiber laser is a type of optical laser that includes a clad fiber rather than a rod, a slab, or a disk. Fiber lasers reflect light through an optical cavity such that a stream of photons stimulates atoms in a fiber that store and release light energy at useful wavelengths. Fiber type, core size, numerical aperture, refractive index, and doping of the fiber contribute to the range and possibilities of light propagation using fiber lasers. A fiber laser may include a core surrounded by a cladding and a protective coating. The core may have a different refractive index than the cladding. Depending on size, refractive index, and wavelength, the core may be single mode or multi-mode although single mode is preferred for many applications. The core may be made of a variety of materials including well-known silica-based materials. The core may include a dopant from the lanthanide series of chemicals including Erbium or Ytterbium that release light energy at useful wavelengths. A fiber laser may be illuminated by a light source, e.g., a laser diode. A light source may be a single diode, an array of diodes, or many separate pump diodes, each with a fiber going into a coupler. A fiber laser may be used in a variety of applications including welding heavy sheets of metal, cutting high-strength steel used to produce automobiles, cutting and drilling concrete, and microscale and nanoscale machining.
In some applications, a fiber laser may have a length between several millimeters and hundreds of meters, most commonly in the 1-30 meter range. A fiber laser may release heat during operation that requires efficient heat removal to avoid damaging core, cladding, or buffer material. Laser systems may necessitate cooling to improve performance, avoid malfunction, and extend product life. As the amount of laser power increases so does the need to remove larger amounts of heat from the laser system to avoid overheating components that may change their operating characteristics. An increase in temperature may result in an increase in laser wavelength and decrease on power that may compromise a laser system's performance. Since the laser wavelength increases and power decreases with an increase in temperature, the temperature must be uniform throughout the system's laser diode arrays to achieve high overall optical conversion efficiency. Laser diode reliability also decreases with increasing temperature, e.g., lifetime decreases by approximately half for every 10° C. increase in temperature in some instances.
Referring to FIGS. 1A-C, a fiber laser 30 may be coiled into a coil and placed within grooves 36 of a plate 32. Plate 32 may be made of any material known to a person of ordinary skill in the art, e.g., metal, plastic, and the like. Grooves 36 may be machined into plate 32 in some examples. Grooves 36 may be sized to receive fiber laser 30, as shown in FIG. 1B. Fiber laser 30 may be coiled in a plane around grooves 36 of plate 32. Alternatively, as shown in FIG. 1C, fiber laser 30 may be coiled vertically around spool 34.
FIG. 2 diagrams a cooling plate 200 that may be used with the coiled fiber laser of FIG. 1. Cooling plate 200 may include a channel formed to receive a tubing 205. The channel may be formed on the cooling plate 200 in a continuous manner alternating from right to left to right to left (or up to down to up to down) as shown in FIG. 2. The channel may include straight portions connected by curved portions. The tubing 105 may have an inlet end and an outlet end that extend beyond an edge of cooling plate 200. A coolant may be fed into the inlet end to discharge from the outlet end.
Cooling plate 200 may include any thermally conductive material known to a person of ordinary skill in the art. However, a cooling plate 200 may be made from a different material than the tubing 205. For instance, the tubing 205 may be made from a first material having excellent thermal transfer capability, such as copper. However, the cooling plate 200 may be made from a second different material (such as aluminum) in order to enable inexpensive channel machining and/or for other reasons related to channel machining processes. The thermal transfer capability of the second different material may not be the same as the first material (e.g., may be lower), which may be an acceptable design tradeoffs for some applications to enable the inexpensive channel etching and/or for other reasons related to channel etching processes.
The cooling plate 100 may have a front face (illustrated) and a back face. In a laser system, a front face of the cooling plate 100 may be in contact with any surface of the plate 32 (FIG. 1A), e.g., the front surface (illustrated) of the plate 32, for dissipating released heat of the fiber laser in the grooves 36 of the plate 32. However, a need remains for more effective mechanisms than such a system to remove heat and cool laser systems.